Core A of the proposed Program Project Grant (PPG) III provides four types of services to the projects: body composition, functional, and quality of life measurements; guidance for appropriate method selection; advice on interpretation of results; and collaborative development of new body composition methods and models. Body composition methods and measurements available to investigators in the projects include: in vivo neutron activation analysis (IVNA) for whole-body N, C, and O; whole-body and regional magnetic resonance imaging (MRI)/spectroscopy for all major tissue-system level body composition components and tissue lipids in humans and animals; whole- body and regional 40K for total body and forearm potassium; dual energy x-ray absorptiometry for whole-body and regional soft tissue and bone mineral; body volume by hydrodensitometry and air plethysmography; deuterium and bromide dilution volumes for total body and extracellular water; bioimpedance analysis (BIA) for resistance and reactance of whole-body regions, and isolated tissues; and anthropometry. Core Unit A has grown and developed substantially over this cycle of the PPG. New space was provided by the Hospital for expanded and new facilities including an IVNA, MRI Analysis, BIA, and Regional 40K Laboratories. The new Core C grew up of the growing and productive data analysis and modeling efforts of the present members of Core A. Core C grew out of the growing and productive data analysis and modeling efforts of the present members of Core A. Close collaborations and interactions with Core B members are leading to new and innovative method development and to cross-validation of state-of-the art methods (e.g., IVNA) transferred from their Department of Energy development site at Core C Brookhaven National Laboratory to Core A at St. Luke's- Roosevelt Hospital. An important extension of Core A projects and collaborations is the association with Department of Biomedical Engineering and collaborative projects at University's high-field strength Hatch MRI facility. The Core's productivity is evident not only in the large number of project-related measurements, but in the many peer-reviewed body composition, functional, and quality of life papers authored by Core members and their collaborators. The large number and diversity of proposed measurements reflect the Core's central role in this overall proposed program.